It is well-recognized that the microenvironment of hemopoietic tissues plays an important role in supporting and/or regulating hemopoietic progenitor cell lodgment, proliferation, and differentiation. However, the relative roles of resident stromal cells, short-range humoral factors (e.g. autocrine or paracrine growth factors) produced within the hemopoietic microenvironment, and extracellular matrix components in regulating hemopoiesis is unknown. The purpose of this project is to define the role of the extracellular matrix in supporting and/or regulating hematopoiesis. In order to study this problem the composition and function of normal murine bone/bone marrow and splenic extracellular matrix will be examined and a multi-pronged attempt will be made to define the specific biochemical basis for the hemopoietic microenvironmental defect in S1/S1d mice. One aspect of the project will involve biochemical analysis of the extracellular matrix from hemopoietic tissues of normal and S1/S1d bone marrow cells and +/+ and S1S1d cloned stromal cell lines in vitro will be analyzed. In a later set of studies the ability of hemopoietic progenitors to grow in long term cultures in which the culture dishes have been coated with extracellular matrix or fractions of extracellular matrix derived from normal or abnormal mice will be determined. In order to determine the specific defect(s) responsible for abnormal hemopoiesis in S1/S1d mice 2-dimensional gel electrophoresis and high pressure liquid chromatography will be used to discover abnormal or missing protein(s) in the extracellular matrix from S1/S1d hemopoietic tissues and in vitro cultures. Also attempts will be made to produce monoclonal antibodies against the extracellular matrix components of interest in normal and/or S1/S1d mice. Finally, extracellular matrix prepared from normal mouse spleen and bone marrow or from the stromal layer of long term marrow cultures will be implanted into S1/S1d mice in an attempt to correct their defective hemopoiesis. These studies should yield valuable information about components of the extracellular matrix that are crucial in supporting normal hematopoiesis. Hopefully these studies also will improve knowledge of the role that microenvironmental defects may play in causing hematopoietic failure.